In its report, launched today, Lord Adonis said: “We urge the Mayor and central government to take forward preparations for Crossrail 2, including a credible funding plan embracing the public and private sectors, with a view to construction in the 2020s.

“London has opened only one and a half new underground lines since the Second World War (the Victoria line and the Jubilee Line Extension).

“Crossrail 2 will be as essential as Crossrail 1 for London to provide jobs and prosperity in the next generation.”

They also said the need for Crossrail 2 has become greater since the Government decided to press ahead with a new high-speed rail link to Birmingham and the North (High Speed 2, or HS2) – which would put more strain on Euston station.

Boris: "There is no time to lose"

Mr Johnson said: “The case for the construction of Crossrail 2 is incontestable and is made forcibly in this report.

"Over the next 20 years London’s population is forecast to expand to levels that will clog the Tube and rail arteries of our great city if we do not provide more capacity.

"There is no time to lose and my team will work closely with London First and others on developing plans for this vital railway.”

Network Rail have also thrown their support behind Crossrail 2.

The rail operator's chief executive, David Higgins, said: “Our projections show that, by 2031, we will need to accommodate 36 per cent more commuters into London each day.

"Network Rail is already delivering the biggest capacity improvement programme since the Victorian era, but even that will not be enough on some routes.

“A regional Crossrail 2 scheme will provide the capacity we need to provide for the commuters of the future, providing extra capacity to and through central London and easing overcrowding on the already congested routes into Waterloo and Liverpool Street.”

The proposal for the route is set to be reviewed early next year by the Department for Transport.